The invention relates to a hybrid drive train for a motor vehicle, having an internal combustion engine for making available internal-combustion-engine drive power, a multi-step transmission having a transmission input and a transmission output, wherein the transmission input can be connected to the internal combustion engine, and wherein the multi-step transmission is designed to set up a multiplicity of different forward gear ratios, and an electric machine for making available electromotive drive power.
In addition, the present invention relates to a motor vehicle having such a hybrid drive train, and to a method for carrying out a gear change in a hybrid drive train.
Hybrid drive trains for motor vehicles are known in different embodiments. In many hybrid drive trains an electric machine is connected to a transmission input. Hybrid drive trains of this type permit the electric machine to be used for boosting or else for purely electric drive. In this case, all the forward gear ratios of the multi-step transmission can be used in the electric driving mode. However, in this case the electric machine cannot be used to make available tractive force assistance during gear changes. This is possible in such hybrid drive trains in which the electric machine is connected to the output of the multi-step transmission. However, in this case a purely electric driving mode can be used only with a single transmission ratio. In addition, charging in the stationary state (using the electric machine as a generator for charging an electric energy store when the vehicle is stationary) is generally not possible.
In addition, hybrid drive trains are also known in which the multi-step transmission is embodied as a double-clutch transmission. Such transmissions in themselves already permit a gearshift without interruption of the tractive force. In this context it is known, for example, to connect an electric machine to one of the two component transmissions of such a double-clutch transmission, generally to the transmission input. However, hybrid drive trains of this type are very complex and many functions are carried out in duplicate.
Document DE 197 47 265 A1 discloses a hybrid drive train in which no separate gear set for the reverse driving mode is set up in the multi-step transmission, with the result that reverse travel is only possible by means of an electric motor.
Document DE 10 2005 048 938 A1 discloses a hybrid drive train having a double-clutch transmission, wherein an electric machine can be effectively connected both to a first and a second input shaft via an additionally provided transmission.
Document EP 1 972 481 A1 discloses a hybrid drive train in which a gear-shift component transmission has an input shaft and an output shaft, wherein, for example, uneven gear ratios are assigned to the first component transmission. In addition, the drive train contains a second gear-shift component transmission having an input shaft and an output shaft, wherein, for example, the even gear ratios are assigned to this component transmission. The input shaft of the first gear-shift component transmission can be coupled to the internal combustion engine via a starter clutch. The input shaft of the second gear-shift component transmission has a drive connection to the electric machine. In addition, the two input shafts can be connected to one another in a rotationally fixed fashion via a coupling unit.
Finally, document DE 196 12 690 C1 discloses a drive train having an automated transmission which is embodied as a range-change transmission with a first transmission group and a downstream second transmission group.